It is an unusual sentence. I suppose Craig's answer is correct, but I can't remember ever hearing someone use "slug" as a verb with that meaning. I would say, don't think about it too much. He is basically walking down the hall.

Yeah, as other said. . . I doesn't really make sense. I think you just have to accept it as creative use of language.

Slug as a verb is what happens when you hit someone or someone. If you've ever seen the Peanuts comics, Lucy often says to Charlie Brown: "I oughta SLUG you." She means, she should hit him. Slug as a verb is also what happens when you drink something. To slug back a tall glass of water means you didn't consider your manners, you gulped it down. So for this example, "slug myself", I'm sorry but I'm going to say it's incorrectly used. A person can be described or compared to a slug, but it's a bit like this sentence should not use this word and instead use "drag". If someone is "sluggish" meaning they are lazy and moving slowly, it would make sense that they "drag" themselves down a hall. The example in the sentence is strange.

Slug has various meanings. In this case it acts as a verb and means to move slowly.